"Unlike a running back, where you can have multiple guys running the rock and they're able to tap out, a quarterback can't do that. He needs to be able to get the signals in and run the next play in a limited amount of time even though he may be seriously injured."

Griffin's health has been heavily debated in his return from knee reconstruction surgery, with his numbers – 59.2% completions, 14 touchdowns, 11 interceptions, 28 sacks taken, 372 rushing yards on 70 attempts – worse across the board in his second NFL season.

San Francisco 49ers linebacker Ahmad Brooks provided perhaps the most damning assessment after last week's blowout win over the Redskins, telling CSN Washington that everyone can see Griffin "shouldn't be playing" at all.

Clarkson thinks the problem may be as much mental as physical after Griffin (6-foot-2, 217 pounds) got hurt last year in an offense that exposed him to more punishment that traditional pocket passers take.

"He's just a shell of himself, and it's only taken a year," said Clarkson, who has worked with Pittsburgh Steelers quarterback Ben Roethlisberger, among others.

"In the National Football League, they are trained assassins and they will make cowards of all those quarterbacks that are in that system. Year 2, they don't want to be a part of it.

"Even (Carolina Panthers quarterback) Cam Newton, as big as he was (6-5, 245), there was a major drop-off from Year 1 to Year 2. He has become a lot more effective by using a run as an alternative, and not the primary or secondary option."

Newton is enjoying his best season for the 8-3 Panthers – and running less than ever. His 77 attempts puts him on pace for 112 over the season, down from 126 in his rookie year of 2011 and 127 in 2012. His completion percentage (61.7%) and passer rating (88.3) are career bests.